Vapor phase methods such as sputtering or CVD and liquid phase methods such as sol-gel methods have been used as methods for producing various types of oxide films, but they have been limited in the following ways.
Vapor phase methods accomplish film formation on substrates in the vapor phase and therefore require costly equipment in order to achieve a vacuum system. Means are also necessary for heating the substrate prior to film formation. It is also difficult to form films on substrates with irregularities or curved surfaces.
Sol-gel methods, as liquid phase methods, require firing after application and therefore result in generation of cracks and dispersion of metal from the substrate. Because of the volatile portion, it is difficult to form a dense coating.
One liquid phase method wherein an aqueous fluorine compound solution such as fluoro-complex ion is used, known as liquid phase deposition, does not require costly equipment to achieve a vacuum, and allows film formation without heating the substrate to high temperature while also allowing formation of thin films on irregularly-shaped substrates. However, because the solutions are corrosive, this method is mainly employed for substrates of non-metal materials, such as glass, polymer materials and ceramics.
In contrast, Japanese Unexamined Patent Publication SHO No. 64-8296 proposes forming a silicon dioxide film on a substrate of a metal, alloy, semiconductor substrate or the like which is at least partially conductive on the surface. As regards the effect on the substrate, however, the text merely states that “it is also possible to add boric acid or aluminum to the treatment solution in order to prevent etching”, and this alone is insufficient. Also, an article by Nitta, S. et al. in Zairyo [Materials], Vol.43, No.494, pp.1437-1443(1994) describes contacting aluminum with a stainless steel substrate and immersing it in a solution for deposition, but hydrogen gas generating reaction occurs violently on the substrate surface due to the solution pH, thereby hampering efforts to form a complete coating.
According to one aspect of the present invention, therefore, it is an object to rapidly form oxide and/or hydroxide films unachievable by the prior art, on metal materials with various surface shapes without heat treatment or with only low-temperature heat treatment, and to thereby provide metal oxide and/or metal hydroxide coated metal materials.
In the liquid phase method known as liquid phase deposition, wherein an aqueous fluorine compound solution such as fluoro-complex ion is used, the low film formation speed, resulting in a long time of several dozen minutes for film formation, has been a drawback as described in the examples of Japanese Patent No. 2828359 and elsewhere.
According to a second aspect of the invention, therefore, it is an object to rapidly form oxide and/or hydroxide films unachievable by the prior art, on conductive materials without heat treatment or with only low-temperature heat treatment, and to thereby provide metal oxide and/or metal hydroxide coated conductive materials.